Glass containers, although aesthetically desirable for many applications, sometimes present severe safety problems especially when the contents of these containers are pressurized, as is the case of carbonated beverages such as soft drinks and beer. It is known that when glass bottles containing such carbonated beverages are dropped, there is a significant danger of not only breaking of the bottle but also of scattering of the fragments of the broken bottle. Many times the real danger in the breaking of such a bottle is not the actual breaking itself but rather the scattering of glass fragments caused by the impact.
In attempting to solve this problem of the scattering of glass fragments, the prior art has employed various coatings and coating procedures. One limitation on the use of many particular coating materials is the fact that many glass containers must be "returnable," i.e., returned by the customer to the bottler for cleaning, sterilization, and refill. Indeed, with the present emphasis on materials conservation, it is of even greater importance that any coating applied to a glass bottle be such that it is not substantially removed when subjected to the cleaning and sterilization procedures at a carbonated beverage bottling plant.
An attempt to solve the above problems of the prior art is disclosed in U.S. Pat. No. 3,823,032.
This patent discloses a glass bottle which is coated on its outer surface by two layers referred to as an inner layer and an outer layer. The inner layer can be a thermoplastic elastomer. However, the inner layer is required to exhibit a minimum adhesion to the glass bottle surface and employs an anti-bonding agent to achieve this affect. When the thermoplastic elastomer is applied it is heated to only 120.degree. C. for 30 minutes in one instance and at room temperature in another instance. Such temperatures are acceptable in the context of this patent but are not suitable when good adhesion is sought to be obtained between the glass bottle and the coating.
Glass containers have been rendered fragment retentive by applying a two layer coating to the external surface thereof as illustrated by commonly assigned U.S. Pat. No. 4,171,056 in the name of M. Hannon and A. Forschirm entitled "Coated Bottle and Method of Coating." The first or inner layer is applied as a non-tacky powder particle composite which includes unhydrogenated and preferably hydrogenated thermoplastic elastomer block copolymers used in combination with a specifically defined melt flow modifier. The powder particle composite is electrostatically sprayed onto the external surface of the glass container and baked at temperatures of about 180.degree. to about 300.degree. C. for about 10 to about 30 minutes. These temperatures are necessary to assure fusion of the composite powder particles to form a continuous nonparticulate layer. At temperatures below 180.degree. C. complete fusion would not occur and the coating would be discontinuous, weak, and exhibit a poor appearance.
An outer coat of a synthetic resin such as epoxy resins, polyurethanes, polycarbonates, polyesters, polystyrenes, ethylene/vinyl acetate copolymers, acrylic acid, homopolymers and copolymers is then applied to substantially the entire outer surface of the inner coat and part of the glass container surface. The present invention, which does not employ hydrogenated thermoplastic elastomers, requires lower bake temperatures, and exhibits good adhesion to the glass container surface when exposed to an alkaline wash.
U.S. Pat. No. 4,163,031 in the name of M. Hannon and A. Forschirm entitled "Powder Composition and Method" is directed to a powder composition useful for coating applications comprising a melt blend mixture of a thermoplastic elastomer block copolymer which is selectively hydrogenated to at least some degree and at least one melt flow modifier.
U.S. Pat. No. 4,201,834 in the name of M. Hannon and R. Green entitled "Powder Composition and Method of Preparation" is directed to the powder composition of composite non-tacky powder particles employed in the method of U.S. Pat. No. 4,171,056 discussed above.
The search has continued for novel coatings and coating procedures for glass containers wherein the coated glass container is both fragment retentive and returnable. This invention was made as a result of that search.
It is an object of the present invention to provide glass containers which are fragment retentive.
Another object of the present invention is to provide glass containers which are returnable, i.e., resistant to delamination of the thermoplastic elastomer coating when subjected to an alkaline wash.
Still another object of the present invention is to provide a process for preparing glass containers which are both fragment retentive and returnable.
Other objects and advantages of the present invention will become apparent from the following summary and description of the preferred embodiments of the present invention.